| 摘要 |
PROBLEM TO BE SOLVED: To provide a free-cutting steel which contains the carbonitrides of Ti and/or Zr as inclusions, and has excellent lathe and drill machinability. SOLUTION: The free-cutting steel has an alloy composition containing, by mass, 0.05 to 0.80% C, 0.01 to 2.5% Si, 0.1 to 3.5% Mn, 0.03 to 1.2% Ti+0.52Zr and 0.015 to 0.6% S, and the balance Fe with inevitable impurities, and in which the contents of Ti, Zr and S satisfy the condition of (Ti+0.52Zr)/S <2. The steel containing 0.0005 to 0.02% Ca and/or 0.0003 to 0.02% Mg exhibits more excellent machinability.
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